Mechanically cycled ink jet printer

ABSTRACT

A mechanically cycled ink jet printer nozzle, through which a stream of ink passes and from which there issues a stream of droplets of ink, is laterally vibrated to cause the stream of droplets to follow a cyclic trajectory or pattern such as a sine wave. Droplets in portions of the pattern then are selected to remain uncharged and impinge a document to print thereon. For nonselected portions, the droplets are charged and deflected to a catcher to avoid printing.

, 1 States Patent [191 Hecht etal.

[ 1 Dec. 3, 1974 r 22 Filed:

[5 MECHANICALLY CYCLED INK JET PRINTER [75] Inventors: Richard M. Hecht; Hubert l).

Faulkner, both of Dallas, Tex.

[73] Assignee: Recognition Equipment,

Incorporated, Irving, Tex.

Sept. 3, 1971 [21] Appl. No.: 177,587

[52] US. Cl. 346/75 [51] Int. Cl. 601d 15/18 [58] Field of Search 346/1, 75

[56] References Cited UNITED STATES PATENTS 2,674,652 4/1954 Johnson et al 178/23 3,404,221 10/1968 Loughren 346/75 X 3,500,436 3/1970 Nordin 346/75 3,596,275 7/1971 Sweet 346/1 3,596,276 7/1971 Lovelady et'al. 346/1 3,737,914 ,6/1973 Hertz H346/75 OTHER PUBLICATIONS Hertz et 211.; A Method For the Intensity Modulation of a Recording INR .let and Its Applications; Acta Univ. Lond; Sec. 2, No. 15 pp. 1-16, 1967.

- Primary Examiner-Joseph W. Hartary Attorney, Agent, or Firm-Richards. Medlock Harris &

[5 7] ABSTRACT A mechanically cycled ink jet printer nozzle, through which a stream of ink passes and from which there issues a stream of droplets of ink, is laterally vibrated to cause the stream of droplets to follow a cyclic trajectory or pattern such as a sine wave. Droplets in portions of the pattern then are selected to remain uncharged and impinge a document to print thereon. For nonselected portions, the droplets are charged and deflected to a catcher to avoid printing.

4 Claims, 10 Drawing Figures TO FIG. 3

TO FIG.3

CONSTANT CURRENT SOURCE PATENTKL 5E3 74 SHEET 1 BF Q CONSTANT CURRENT SOURCE FIG. 2

KmE-ZDOQ Plumm t: 31914 suwuurg FIG. 10

MECHANICALLY CYCLEI) INK JET PRINTER This invention relates to a mechanically cycled ink jet printer nozzle cooperating with means for selectively charging droplets issuing therefrom during selected portions of the mechanical cycle for control of the trajectory of the droplets to permit some to impinge a document and others to be intercepted before impingement.

Ink jet printers heretofore have involved the projection of charged droplets and the deflection of the droplets in an electrostatic field by programming the magnitude of charge on the droplets. Thus, control of charging systems has been complex. It has been found, however, that the same results can be obtained by mechanically cycling the nozzle from which the. droplets immerge so that the trajectory of the droplets is cyclically altered. If then the droplet charging field is turned on and off during selective portions of each cycle of the nozzle trajectory, the charged droplets may be subject to a deflecting field which will direct the charged droplets to a'catcher and permit only noncharged droplets to impinge a document.

The printing operation may be carried out by the simple switching on and off of the droplet charging field between zero and a predetermined gating level. Eliminated are the program requirements for controlof the charging voltage. Such systems greatly simplify the control system while permitting printing of bar codes as well as alphanumeric characters.

In accordance with the preferred embodiment of the invention, an ink jet printer is provided for printing a line of data on a document during relative movement between the printer and the document. The nozzle structure is actuated to project a stream of ink droplets toward the document. Means are provided for mechanically cycling the nozzle laterally or perpendicularly to the axis of the nozzle cyclically to alter the direction of travel of successive droplets. Means are provided for selectively charging the drops issuing from the nozzle to a potential above a predetermined level. Means are also provided to establish an electrostatic field in the zone through which the droplets pass. Means synchronized with the vibration of the nozzle selectively energizes the charging means to charge droplets in those portions of the pattern not desired on the document.

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side view of one embodiment of the writing portion of a printer embodying the present invention;

FIG. 2 is a top view of the unit of FIG. 1;

FIG. 3 is a circuit diagram of the control system for the printer of FIG. 1;

FIG. 4 is a diagram representing a sine wave pattern produced by vibration of the nozzle support of FIG. 1;

FIG. 5 is a diagram illustrating coding of the circuit of FIG. 2 for selecting the portions of the pattern to be printed;

FIG. 6 illustrates a mode of imparting mechanical vibrations to the nozzle by contact with a serrated surface; 7

the nozzle through a torsion member;

FIG. 8 illustrates the system mounted for translation of the printer relative to a fixed document;

FIG. 9 illustrates a further modification for translation of the printer relative to a fixed document; and

FIG. 10 illustrates printing alphanumeric characters in accordance with the present invention.

Referring now to FIGS. 1 and 2, an ink jet printer is illustrated wherein a center supported bar I0 has a nozzle 11 secured to the end of a tube 12 through which ink is supplied to nozzle 11. The tube 12 is secured by a clamp 13 to one side of bar 10 and leads to a pressurized ink supply (not shown) but connected to the end 14.

in response to energization of the crystal 16 breaks the stream of ink 17 which issues from the nozzle 11 into discrete uniform droplets.

Support members 18 provide a mounting for bar 10 such that bar 10 is supported at a vibration node. The mounting of bar 10 and the supply of ink therefor generally will be as found in systems described in Instruction Manual Ink Jet Printer, (1970) by Recognition Equipment Incorporated, Dallas, Tex.

In accordance with the present invention, the bar 10 is mechanically cycled to produce vibration in a second mode in order to cause the stream of ink droplets to trace a cyclic trajectory 20 such as a sine wave. More particularly, as illustrated in FIG. 1, coils 21a and 21b are mounted on opposite sides of the bar 10. The ends of magnetic core 23 for coils 21a and 21b face the surface of the bar 10 at a location spaced from the nodal mounting.

In accordance with one embodiment of the invention, coils 21a and 21b were energized at a frequency of'600 cycles per secondfln contrast, the crystals 16 were energized at 48,000 cycles per second.

As shown in FIG. 1 the stream of ink droplets issuing from nozzle 11 pass through a fork shaped pair of charging plates 24 and 25. Charging plates are electrically common and are connected in a circuit, later to be described, such that they will be either at zero potential or at a significant potential above ground. The ink supply and the ink in the stream of ink droplets initially are always at ground potential.

A pair of deflecting plates 26 and 27 are maintained at a predetermined constant potential.

An ink catcher 29 is mounted in front of a document 28 adjacent but out of the normal path of the sinusoidal stream 20.

In accordance with the present invention the charging plates 24 and 25 are selectively connected to a potential source to establish successive electrostatic fields. As the droplets pass through such field, they will be given an electric charge. They are charged only during those portions of the sine wave that are not to appear on the document 28. When the droplets are charged to a predetermined potential, the median 20a of the stream 20 is displaced to location 2% so that all charged droplets are caught by the catcher 29 and directed to an excess ink reservoir.

By imparting mechanical motion to produce a cyclic pattern in the trajectory of the droplets such as the sine wave illustrated in FIG. I, a greatly simplified writing terns where the voltage on the charging plates 24 and 25 had to be programmed to different levels for each of the successive drops permitted to impinge the document. The present invention permits merely switching on a constant voltage to the charging plates 24 and 25 so that all unwanted portions of the cyclic trajectory are directed to the catcher 29.

The invention thus far described is particularly useful in applying bar codes to a document 28. It will be understood from the following description of, the control circuit that different modes of bar coding may be accommodated. For example, some systems now in operation require a binary bar code to consist of long bars representing a one and half-length or short bars to represent zeros. In other systems the presence of a bar indicates a one and the absence of a bar indicates zero. Either type coding may be accommodated. Further, it will be shown that this type of system may be employed for writing alphanumeric characters with the present simplified control system.

Uniform charging of droplets is preferably accomplished in accordance with the phaseadjustingmethod described and claimed in U.S. Pat. No. 3,596,276 entitled Ink Jet Printer With Droplet Phase Control Means", filed by Kenneth T. Lovelady and Robert B. McJohnson and assigned to the same assignee as this application.

Referring now to FIG. 3, a control system has been shown wherein the printer of FIGS. 1 and 2 is controlled to apply bar codes to a document 28 as it moves past printer bar 10. Velocities of the document may be on the order of 30 inches per second. The printer is so controlled in this embodiment to accommodate an address optically read from a lettersuch as document 28, analyzed and converted to a suitable code by optical character recognition (OCR) equipment (not shown). The code is then translated in the control circuit of FIG. 3 to print a bar code representation of the address in response to operation of the system shown in FIG. 3.

In FIG. 3, primary timing control is by way ofa clock 30. The clock 30 operates in this embodiment at 4,800 cycles per second. The output line 31 leads to a pair of binary counters 32 and 33. The counters 32 and 33 serve to divide the input signal on line 31 so that on each one of the output lines pulses are produced at different fractional values of the input frequency. For example, the signal on lead D of counters 32 and 33 is equal to 1/16 of the input frequency, 300 pulses per second.

The outputs of the counters 32 and 33 are selectively connected by way of NAND gates 34 and 35 toa NAND gate 36. The output of NAND gate 36 is connected by way of NAND gate 37 and inverter 38 to a high voltage amplifier 39. The output of amplifier 39 is then applied to the charging plates 24 and 25, FIGS. 1 and 2. This voltage is gated off and on to control the portions of the droplet trajectory which impinge document 28 and the portions to be directed to the catcher 29. It will be noted from FIG. 2 that a light emitting diode 50 is positioned on one side of document 28 along the path of travel thereof. A light sensor transistor 51 is positioned on the side opposite diode 50. The collector of sensor 50 is connected to a voltage comparator 52 whose output is applied by way of an amplifier-inverter 53 to control a shift register 54. The

comparator 52 provides a 0-1 output depending on whether or not a document is present between source and sensor 51.

Selected outputs from the shift register 54 are connected by way of a NAND gate 55 to a NAND gate 56 and thence to a second input of NAND gate 37. By this means, amplifier 39 may be energized only when a document is present in the field of the printer and then only at a selected location on the document. More particularly, the shift register 54 permits introduction of a selected delay in its output. This delay compensates for the space between the location of the document sensor units 50 and 51 and the actual location along the path of travel of the document of bar 10. An additional delay will be introduced to accommodate any desired margin on the document before the printing of bar codes is to occur.

As illustrated in FIG. 3, the first and last outputs of the shift register are connected to a NAND gate 55 to set the delay. Any desired delay can be set by selecting outputs from a shift register system for application of an enable pulse to the NAND gate 37. Thus, in the system thus far described, the amplifier 39 is conditioned to be turned on to apply a charging voltage to the charging plates 24 and 25 to print a selected fraction of a wave that would be traced by the stream of droplets were none of the droplets charged. All droplets in the wave except the selected fraction are charged. More particularly, referring to FIG. 4, a sine wave 60 representing the trajectory of stream 20 is divided into eight time segments. In accordance with the invention. long bars are printed on a document by charging all of the cycle except the fourth and, fifth segments. A short bar is formed by charging all of the droplets forming the sinusoidal waveform except those in the fifth segment.

In accordance with the invention, the time occurrence of each of the eight segments of the waveform is represented by a code at the outputs of counters 32 and 33. The states of the counter outputs B, C and D for each of the segments are illustrated in FIG. 4. At a time corresponding with the first segment of the waveform, the counter outputs are all zero. For the second segment, the states of counter output lines B, C and D are B=l, C=0, and D=0. Lines B, C and D are selected and employed as will now be explained. Because of a phase shift involved between the excitation of the coils 21a-21b and the motion of the bar 10, the mechanical waveform is delayed 90 from the electrical waveform to the time position of waveform 61. Thus, with respect to the outputs B, C and D of counter 32 during the intervals corresponding with the fourth segment of waveform 61, the states are B=l, C=0, and D=l and for the fifth segment B=0, C=l, and D=l.

Lines B, C and D are connected to gate 34. Data input line X is also connected to gate 34. Line X leads from an optical character reader which reads data from document 28 and translates the same into a sequence of 0 and 1 states on line X which represents the bar code sequence to be printed. If a long bar is to be printed, line X will be true as will linesB, C and D. This will result in plates 24 and 25 being turned on during the fourth segment of waveform 61.

Lines B, Cand D are connected to gate 35. They will all be true during the-fifth segment so that a short bar segment will be printed on each cycle.

FIGS. 2 and 3 also illustrate the drive system for the bar 10. It will be noted that two coils 22a and 22b are connected to the input of a full. wave rectifying amplifier 100 to produce a DC. voltage at terminal 101 which is proportional in amplitude to the amplitude of lateral vibration of the bar 10. This signal is then applied by way of a scale and offset circuit 102 as an AGC signal to a differential amplifier 103. The amplifier 103 is pulsed by a 300 cycle clock pulse applied from line D from counter 32 to one input of the amplifier 103 and by way of inverter 105 to the other input of the amplifier 103.

The output of amplifier 103 then energizes a driver circuit 106 for coils 21a-21b. The driver circuit 106 is operated in a semi push-pull mode. The waveform of the voltage at the output of the amplifier 103 is almost a square wave. The waveform at the output of driver circuit 106 is applied to the coils2la-2llb and is'illustrated by the graph associated with the output lines 107 and 108. By this means the bar is dimensioned and driven at 300 cycles which is at or close to its resonant frequency. Thus, the frequency is fixed and the phase relation with respect to thesignals from the binary counters 32 and 33 is known- In practice, the connections between counter 32 and the amplifier 39 may be selected by trial and error.

That is, a selection may be made until the voltage is removed from the charging plates 24-25 during the sub stantially linear portion of the trajectory of the waveform of FIG. 4 as represented by the fourth and fifth segments thereof. In the example given, lines'B, C and D were chosen because the states thereon conveniently relate to and provide for selection or designationof segments 4 and 5 of waveform 61.

In systems having different physical constants, different counter outputs may be found necessary to provide for selection of the desired segments.

Counter 33 in this embodiment is used only to provide an input to shift register 54. Each cycle is divided into sixteenth segments for more precise selection of the portion to be printed. Indeed, for alphanumeric printing, finer division than sixteenths may be necessary. In any event, the control may be as shown in FIG. 3. For printing a 5 X 7 alphanumeric matrix, for example, the linear portion of the trajectory (segments 4 and 5 of waveform 61) would be divided into seven subdivisions. In such case, there would be seven gates rather than the two gates 34 and 35.

Referring now to FIG. 5, a sine wave has been illustrated in dotted lines with the bar portions which are selectively printed on the document shown solid. The frequency of the drive signals applied to the bar 10 and the speed at which document 28 travels are coordinated such that the bars will occur at a desired spacing. The amplitude of vibration and the distance from the document thus determine the amplitude of the trajectory as selected to give the desired bar heights.

By way of example and not by way of limitation, the embodiment of the control circuit shown in FIG. 3 employed the following components:

amplifier 39 Recognition Equipment Incorporated Standard Part. No. 6053290 inverter 38 Motorola MC836 NAND gate 37 Motorola MC846 NAND gate 36 Motorola MC846 NAND gate 35 Texas Instruments SN7420 -Continucd NAND gate 34 Texas Instruments SN7420 NAND gate 56 Motorola MCX46 NAND gate 55 Motorola MC846 comparator 52 National Semiconductor DM8820 amplifierinverter 53 National Semiconductor DM882O diode 50 Texas Instruments X617 sensor SI Texas Instruments L6l2 counters 32-33 Signetics N828l shift register 54 Texas Instruments SN74I64 differential amplifier I03 National Semiconductor LM370 amplifier l06a Signetics N5558 diodes l06b Motorola IN663 transistor I060 Fairchild 2N3643 transistor I061! Fairchild 2N3638 transistor l06e Fairchild 2N49l3 transistor l06f Fairchild 2N4904 resistor l06g 2000 ohms A watt resistor l06h 560 ohms V2 watt resistor I06! l0 ohms 1% watt In FIG. 6, an ink jet unit 200 is mounted on a pivotal support including bars 201. A serrated plate 202 is moved past the jet unit to produce vibration indicated by arrow 203. The document 28 moves past the droplet path to intercept the droplets. As a result, a cyclic wave may be printed on the document.

The charging and deflection and ink catching components of the system have not been shown in FIG. 6. It will be understood, however, that FIG. 6 illustrates a mode of lateral vibration of the ink jet cyclically to vary the trajectory of the droplets. With a droplet stream, the control system may be as in FIGS. 1-3 for selecting portions of the stream to be printed.

In FIG. 7 a further modification for producing lateral vibration of the ink jet has been shown. In this system, a disk 210 is mounted on helical springs 211 and 212. The springs 211 and 212 may be formed of a magnetostrictive or piezoelectric material. Such springs suitable energized will cause the disk 210 to vibrate with nozzle 214 forming part of the vibrating system. Thus, a further means for producing lateral vibration may be employed.

In FIG. 8 the jet system in or a part of a carriage 220 is mounted on a pair of guides 221 and 222. Guide 222 has helical grooves therein which cooperate with a follower (not shown) in the carriage 220 in a manner well known in the art to cause translation of the carriage 220 in the direction of arrow 223 and to return the carriage back to an initial position. In such system, the document 28 is fixed while the system embodying the present invention has its ink jet movable on a carriage.

Here, the charging plates 24 and 25 and the deflection plates 26 and 27 are also illustrated and mounted for movement along with carriage 220.

A further-mode of providing for translation of the printing unit is illustrated in FIG. 9 wherein a carriage 230 is mounted on abeam 231 by means of rollers 232. The carriage is then driven under the control of a belt 233 to reciprocate the carriage as indicated by arrow 234.

In FIG. 10, the printing of alphanumeric characters has been illustrated. In this embodiment, a 5 X 7 matrix is employed. Each drop is then selected in a segmental basis as above described so that any one of the segments of the trajectory waveform may be selected to result in the printing of a drop at a desired location. In this embodiment, the gun 11 projects a stream of droplets in a normal trajectory plane. When printing is not to be permitted, the deflection plates 26 and 27 coopcatcher 29. Document 28 will move in the direction of arrow 270 as the charging plates 24 and 25 are selectively connected and disconnected to the voltage source.

Having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.

What I claim is:

1. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises:

a. a nozzle structure for projecting a stream of ink droplets toward the document, said nozzle structure includes a metal mounting bar,

b. means for mechanically moving the nozzle cyclically in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes a pair of field coils located on opposite sides of said mounting bar, and means for cyclically energizing said coils to repeatedly deflect said mounting'bar between said coils,

c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level,

d. means for establishing a deflecting field in a region through which the droplets pass,

e. an ink catcher adjacent to the path of said droplets,

and

f. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the dropletpattern not desired on the document whereby the reaction of the charged droplets with said field directs said charged droplets into said catcher.

2. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises:

a. a nozzle structure for projecting a stream of ink droplets toward the document, said nozzle structure includes a metal mounting bar;

b. means for mechanically moving the nozzle cyclically at a constant frequency and amplitude in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes:

a pair of field coils located on opposite sides of said mounting bar; and

means for cyclically energizing said coils to repeatedly deflect said mounting bar between said coils;

c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level;

d. means for establishing an electric field in a region through which the droplets pass; and

6. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field prevents said charged droplets from reaching said document.

3. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises:

a. a nozzle structure for projecting a stream of ink droplets toward the document,

b. means for mechanically moving the nozzle cyclically in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes a serrated plate mounted for movement in a direction transverse to the axis of said nozzle whereby contact of the serrations with said nozzle induce cyclic vibrations in said nozzle,

0. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level,

d. means for establishing a deflecting field in a region through which the droplets pass,

e. an ink catcher adjacent to the path of said droplets,

and

f.-control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field directs said charged droplets into said catcher.

4. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises:

a. a nozzle structure for projecting a stream of ink droplets toward the document;

b. means for mechanically moving the nozzle cyclically at a constant frequency and amplitude in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes a serrated plate mounted for movement in a direction transverse to the axis of said nozzle whereby said contact of the serrations with said nozzle induce cyclic vibrations in said nozzle;

c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level;

d. means for establishing an electric field in a region through which the droplets pass; and

e. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field prevents said charged droplets from reaching said document. 

1. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises: a. a nozzle structure for projecting a stream of ink droplets toward the document, said nozzle structure includes a metal mounting bar, b. means for mechanically moving the nozzle cyclically in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes a pair of field coils located on opposite sides of said mounting bar, and means for cyclically energizing said coils to repeatedly deflect said mounting bar between said coils, c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level, d. means for establishing a deflecting field in a region through which the droplets pass, e. an ink catcher adjacent to the path of said droplets, and f. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field directs said charged droplets into said catcher.
 2. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises: a. a nozzle structure for projecting a stream of ink dropletS toward the document, said nozzle structure includes a metal mounting bar; b. means for mechanically moving the nozzle cyclically at a constant frequency and amplitude in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes: a pair of field coils located on opposite sides of said mounting bar; and means for cyclically energizing said coils to repeatedly deflect said mounting bar between said coils; c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level; d. means for establishing an electric field in a region through which the droplets pass; and e. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field prevents said charged droplets from reaching said document.
 3. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises: a. a nozzle structure for projecting a stream of ink droplets toward the document, b. means for mechanically moving the nozzle cyclically in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes a serrated plate mounted for movement in a direction transverse to the axis of said nozzle whereby contact of the serrations with said nozzle induce cyclic vibrations in said nozzle, c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level, d. means for establishing a deflecting field in a region through which the droplets pass, e. an ink catcher adjacent to the path of said droplets, and f. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field directs said charged droplets into said catcher.
 4. An ink jet printer for printing a line of data on a document during relative movement between the printer and the document which comprises: a. a nozzle structure for projecting a stream of ink droplets toward the document; b. means for mechanically moving the nozzle cyclically at a constant frequency and amplitude in a direction lateral to the axis of the nozzle to cyclically alter the direction of travel of successive droplets and produce a droplet pattern, said moving means includes a serrated plate mounted for movement in a direction transverse to the axis of said nozzle whereby said contact of the serrations with said nozzle induce cyclic vibrations in said nozzle; c. means for selectively charging the droplets issuing from the nozzle to a potential above a predetermined level; d. means for establishing an electric field in a region through which the droplets pass; and e. control means synchronized with the movement of the nozzle for selectively energizing said charging means to charge the droplets in those portions of the droplet pattern not desired on the document whereby the reaction of the charged droplets with said field prevents said charged droplets from reaching said document. 